1. Field of the Invention
This application claims a priority based on German application 199 20 190.0 filed May 3, 1999, and the contents of that application are incorporated herein by reference.
This invention relates to inductive angle or linear sensors, more particularly to inductive angle or linear sensors for use on motor vehicles.
2. Background Art
German patent document DE 197 38 836 A1 discloses the measuring principle involved using an angle sensor. FIG. 3 of that German document also illustrates inductive coupling elements having meandering structures.
The output signals of such linear and angle sensors exhibit a certain residual error with respect to a position of the sensor. Such a residual error with respect to a linear sensor is illustrated in FIG. 1. In the Figure, a percentage error of the sensor is shown as a function of a scaled position of an inductive coupling element.
An analysis indicates that this error is caused by a non-linear progression of a magnetic field of the inductive coupling element. The progression is represented in FIG. 2 for a rectangular conductive grid, at a defined distance d.
A sinking of a plateau shown in the drawing, of a measured signal in the measuring direction causes a large part of the error. A six-fold repetition of the error across the measuring path during operation of the sensor results from the angle sensor having three receiving coils divided into six partial areas. The measuring principle of a sensor having several receiving coils is described in German patent document DE 197 38 839 A1.
The magnitude of the error represents a significant limitation to the operational accuracy that can be achieved by a sensor of this type.
It is therefore, an object of this invention to provide an inductive sensor in which an error that arises as a result of non-homogeneity of a magnetic field created by an inductive coupling element is significantly reduced.
According to principles of the present invention, an inductive linear sensor for a motor vehicle includes an oscillator circuit for generating a periodic alternating-voltage signal; an exciting coil coupled to the oscillator circuit; several receiving coils; an evaluating circuit for evaluating signals induced in the receiving coils; and one movable inductive coupling element which influences a strength of inductive coupling between the excitation coil and the receiving coils. In one embodiment of the invention, the inductive coupling element has a substantially rectangular shape but at least one outer boundary line thereof differs from the geometric shape of a straight line.
According another embodiment of the present invention, the inductive coupling element has a meandering conductive grid formed of opposite substantially circular arc sections having radial connecting lines extending between the circular arc sections, with a direction of at least one of the connecting lines differing from a radial direction.
Starting with an uncomplicated geometry of a moveable inductive coupling element having a rectangular conductive grid for a linear sensor, which is analogous to a closed loop for an angle sensor, and with a given geometry of a receiver conductive grid, the geometry the moveable inductive coupling element is purposely changed to achieve a desired result.
By this matching of the geometry of the inductive coupling element, the error is minimized so that, in general, a sensor with more exactness is achieved.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.